Blue tooth Phone Ring

MJM33067

I have touring with nav with an Iphone 3G (lastest software upgrade) paired with car. I want only the phone to ring for incoming calls (as I have certain ringtones for certain people) and to defeat the ringing coming from the car. There is a setting under phone called "Use Vehicle Ringtone", however the car rings whether this is switched on or off. There is also a setting under Volume and Beeps for Ringer Vol (but at lowest level, car ring still sounds). Does anyone know how to make a paired phone only ring on the phone and not the car for incoming calls? Don't know if I'm missing something or if it is problem with Iphone.